Air heater having reverted expanding combustion chamber



Sept. 7, 1948- WJHOLBROOK Y 2,448,595 AIR HEATER HAVING REVERTED EXPANDING I COMBUSTION CHAMBER 2 Sheets-Sheet 1 Filed Sept. 1.6 1944 HOLBROOK 2,448,595

) AIR HEATER mwm EVERTED EXPANDING Filed se c. is, 1944 Sept. 7, 1948.

COMBUST CHAMBER v 2 Sheets-Sheet 2 Patented Sept. 7, 1948 UNITED STATES I PATENT 5 m: amass f Am naa'raa nsvmo aavaarao axrsnn- 1 ma cosmos-non cmmmaa Wallace Bolbrook, m Angelel, Calif.

Applicationsoptember 16, 1944, Serial No. 554,473

9 Claims. (or. 120-110) My invention relates to-air heaters, and among Fig. 7 is a fragmentary secti nal V w throu the objects of my invention are:

First, to provide an air heater having an extremely large heat output in relation to its 1-1 of Fig. 1, showing the fuel nozzle in elevation. Fig. 8 is an enlarged fragmentary sectional view through 8-! of Fig. 7, showing details of weight and size, thereby providing an air heater the fuel nozzle.

for airplanes, or other vehicles where weight an size are primary factors.

Second, to provide an. air heater wherein the heating unit is capable of ignition even under extremely adverse conditions of temperature and altitude; that is, the heater is capable of ready and virtually instantaneous operation even when the starting temperature is as much as sixty-five degrees below zero Fahrenheit, and the altitude is 45,000 feet.

Third, to provide an air heater which incorporates a novel thermostat control element designed to regulate air flow through the combustion passage of theheater particularly during its warming-up period.

Fourth, toprovide an air heater having heat transfer means associated with its combustion passage which efliciently transfers heat to air passing through a separate air duct or passage.

Fifth, to provide an air heater which is designed to burn liquid fuel, preferably asoline,

although it may operate with equal eiliciency on a wide range of liquid or gaseous fuels.

Sixth, to provide an air heater which operates efliciently in'any position; that is, ,on its side, or either end uppermost.

Seventh, to provide an air heater which incorporates a novel electrically operated ignition unit.

Eighth, to provide an air heater wherein the igniter and nozzle are readily accessible for removal and servicing without disturbing the heater installation.

With the above and other objects in view as may appear hereinafter, reference is directed to the accompanying drawing, in which:

Fig. 1 is a longitudinal sectional view of the air heater.

Fig. 2 is an enlarged fragmentary sectional view of the air bypass valve.

Fig. 3 is a transverse sectional view of the air heater taken through 3-3 of Fig. 1.

Fig. 4 is a transverse sectional view thereof taken through 4-4 of Fig. l.

Fig. .5 is an enlarged fragmentary sectional view of the air heater taken through 58 of Fig. 1 showing the thermostat valve and one form of the ignition element Fig. 6 is an enlarged sectional view of a modifled form of ignition element, with the air-heater 65 shown as fragmentary.

Fig. 9 is a diagrammatical view showing the fuel supply system and electrical control system employed in conjunction with the air heater.

My air heater is contained within a cylindrical 10 outer shell i open at its ends. Within the outer shell I is a combustion chamber shell I which is likewise cylindrical but closed at its ends by end members 3 and 4. The end member 4 is protected by a convex bailie disc 4a secured to its inner side. Thebaflle disc la forms therewith a "dead" air space having,- however, superficial communication with the interior of the combustion chamber to insure equalization of pressure.

The combustion chamber shell 2 is supported in concentric relation with the outer shell I by an accordion ring I, that is, a tubular structure formed by pressing the sheet material into zigzag form and ntting it between the two shells. The accordion ring forms channels for the flow 0! air to be heatedrbetween the outer shell I and the combustion chamber shell 2. and extends a substantial portion of the length of the combustion chamber shell. I The channels formed by the accordion ring 6, shell I and shell I tend to straighten the flow of air.

A combustion cone-B is secured in the forward or inner end member 3 of the combustion chamber shell 2. The smaller end of the combustion cone extends forwardly from the end member 3 to a point adjacent to the forward or entering end of the-outer shell i and is closed by and end 'disc I. The other or larger end of the combustion cone 8 extends within the combustion chamber, shell to a point adjacent but spaced from the rearward end member t thereof. The larger end of the cone 6 is supported by tabs Ba bent from the cone to engage the walls of the shell 2.

The combustioncone 8 is intersected tangentially by the flattened inner end of an intake tube II. which extends laterally through the outer shell i. An exhaust tube l2 extends laterally from the combustion chamber shell 2 adjacent its forward end, and likewise projects through the outer shell I. The intake and exhaust tubes are preferably in longitudinal alignment with respect to the outer shell 1. Between the intake tube and the exhaust tube is is formed a ,combust'ion chamber which increases in cross-sectional, 'area.

The combustion cone 6 is so proportioned that the area at its larger end equals the area between this end and the combustion chamber shell. By reason of the tapered form of the combustion cone 8 an annular space is formed between the cone and the combustion chamber shell, which continues to increase from the forward or larger end of the combustion cone to the exhaust tube t2. The combustion chamber can thus be termed a reverted continuously expanding combustion chamber.

An air intake T-fltting comprising a cross-tube l4 and a leg tube I5, is mounted by its leg tube on the outer end of the intake tube II. An exhaust 'r-fitting l8 comprising a cross-tube and a leg tube I8 is fitted by means of its leg tube to the outer end of the exhaust tube 12. The cross-tubes l4 and ll of the T-fittings telescope and are in alignment to form a. common air conduit traversing the intake and exhaust tubes. Between the intake and exhaust tubes there is located in the cross-tube M of the T- iltting l3 an air bypass valve I! in the form of a disc or plate journaled near one side by a stem 28. A spiral spring 2| is provided which is attached to the stem 28 in such a manner that it tends to maintain the valve l3 closed. Air flowing through the air conduit defined by the crosstubes I4 and H, tends to open the valve against the action of the spring 2|.

Within the exhaust tube l2 and the leg tube I8 is positioned a thermostat control valve 22. The thermostat control valve includes a base ring 23 suitably secured within the tube, and a plurality of thermostat petals 24 of triangular form which are secured by their base ends to the ring 23 and extend upwardly to define a pyramid having its apex protruding into the cross-tube il. Normally, the thermostat petals 24 are fiat with their edges in approximate contact with each other.

On heating, the petals curl outwardly from each other to increase the opening through the exhaust tube. While four petals 24 are shown, either a greater or lesser number may be used; even two may be employed by extending the base ring 3 to replace the omitted two petals.

Between the air intake tube I and the forward or smaller end of the combustion cone 8 is a fuel nozzle sleeve 3| which is preferably circumferentially displaced with respect to the intake tube I. The fuel nozzle sleeve 3| extends through the outer shell I. Within the sleeve is positioned a tubular fuel nozzle body 32 having a'threaded portion which closes the sleeve, and terminates at its inner end in a head 33 centered in the combustion cone 8. The forward side of the head 33' is provided with a threaded socket which is closed by a plug 34. The socket communicates with the bore of the fuel nozzle body 32 through a passage 35. The base or rearward end of the socket is provided with a conical nozzle orifice 38 which discharges into a recess 31 formed in the rear side of the head 33. The plug 34'carries a conical needle 38 the apex angle of which is less than the apex angle of thenozzle orifice 38, so

, does not readily clog.

" grounded by a bracket 82.

An igniter tube 4| intersects the combustion cone 8 and extends laterally through the combustion chamber shell 2 and outer shell i. The radially inner end of the igniter tube 4| is provided with a scoop 42 directed into the combustion cone 8. The scoop is preferably semicylindrical and slopes forwardlygtoward the fuel nozzle.

- Within the igniter tube 4| is positioned an igniter element which may take the form of the igniter element 43 shown in Fig. 5, or the igniter element 5| shown in Fig. 6. with reference to Fig. 5, the igniter element 43 comprises a tubular body 44 closed at its radially outer end and provided with a shoulder and screw threads for sealing engagement with the igniter tube 4|. The body 44 receives a core 45 of ceramic material or other heat-resisting material. The core 45 is provided with a helical groove in which is wound a resistance coil 48, one end of which it attached to a terminal 41 which is insulated from and extends through the closed outer end of the body 44. The radially inner end of the core 45 is provided with a socket 48. Within the socket 48 is a filament 43 formed of platinum or other material capable of withstanding high heat. The filament 43 is electrically connected in series with the resistance coil 48, one end of the filament being grounded. The scoop 42 causes an eddy current which-circulates into the socket 48 and carries fuel which, oncontact with the heated filament 48, ignites. The operation of the igniter element will be brought out in more detail hereinafter.

Reference is now directed to the modified igniter element 5| shown in Fig. 6. This igniter comprises a body member 52 which is screw-threaded to the igniter tube 4| and extends outwardly therefrom. Within the body 52 is a solenoid 53 which actuates an armatur 54 extending into the igniter tube 4|. 52 is closed by a cap 55 having a central boss which forms a stop 58 extending into the solenoid 53. A spring 51 is interposed between the stop 58 and the armature 54. The armature 54 is provided with a flange 58 located adjacent the inner end of the solenoid 53. A pig-tail 53 electrically connects the armature in series with the solenoid 53. The armature is guided by an insulation washer 88 which also serves to protect the solenoid 53 from heat. The radially inner end of the armature 54 carries one of a pair of ignition contacts'8l, the other of which is supported and The igniter element 5| is designed to vibrate; When the ignition contacts 8| ar in engagement, the solenoid 53 is energized which causes the armature to break the contacts, ole-energizing the solenoid and allowing the spring 51 to urge the armature to again close the ignition contacts. The solenoid also functions at least in part as an inductive member to increase the current at the moment the contacts disengage to produce a strong are capable of igniting the fuel. The rapidity with which the ignition contacts make and break a circuit, is determined by the constants of the spring 51 and the durationof the are after the contacts are disengaged.

Fuel is supplied to the air heater from a tank H through a pump 12 driven by a motor 13. The fuel,- on leaving the pump, first passes through a strainer or filter 14, then through a pressure regulator valve 15, then in series through a pair of solenoid valves 18 and I1. A bypass line is provided around the solenoid valve 11 and includes an orifice or resistor valve 18. The

The outer end of the body' through the exhaust tube 12.

igniter element 43 or BI is adapted to be controlled through a thermostat switch 19 which is normally closed, but which opens when the tem-: perature within the heater has reached a predetermined amount; for example, 175 F. A main switch 80 is in series with the igniter switch 19 between th igniter switch and a source of electrical energy, not shown. Al'so controlled by the main switch 80 is a low thermostat switch ll which is normally closed, but designed to open at for example, 300 F. A manually operated switch 82 is placed in series with the thermostat switch ill for the purpose of rendering the thermostat switch 8| inoperative when the manual switch is open. The power supply is also connected to a high heat thermostat switch 83 which controls the solenoid valve 18 and motor 13. This switch may, for example, be set to open at 350 F. The temperature values given above are of course arbitrary and may vary considerably, depending upon the location of the thermostats relative to the air heater and the conditions under which it is desired to operate the air heater.

Operation of my air heater is as follows: The main switch 80 is first closed; In the initial condition all the thermostat switches 19, 8| and BI are closed. Consequently, the motor 13 actuates the pump 12 to deliver fuel from the nozzle 36. The air'heater is positioned in an air stream, either a natural air stream if the heater is installed on a vehicle, or an artificially supplied air stream if otherwise mounted.- A portion of e the air stream flows through the outer shell I around the combustion chamber shell 2. A portion of the air stream also flows through the air conduit formed by the cross-tubes i4 and ll of the ,T-fittings. By reason of the air bypass valve i9 a substantial part of the air flowing'through the air conduit is diverted through the intake tube I1 through the combustion chamber formed by the combustion coneB and combustion chamber shell 2, and returned to the air conduit The air is introduced into the combustion chamber tangentially so that it flows therethrough with a swirling movement.

Initially, particularly before ignition, the fuel is in the form of line droplets, some of which impinge on the scoop 42, and by reason of their mass are deflected into contact with the igniter element. Very little of the air itself is so deflected once the pressure in the ignition socket has built up slightly above that in the combustion chamber. This is highly important for in airplane installations the air may be extremely cold, perhaps 65 below zero Fahrenheit, and any substantial circulation'of such cold air across the igniter, would interfere with its operation. Once ,the fuel ignites and the combustion chamber warms up, the fuel particles are more finely divided, if not in actual gaseous form, by the time are rapidly heated and curl outwardly from each other to the dotted line positions shown in Fig. 1.

Although suited for other vehicles or even home use, the air heater is primarily intended for use on airplanes, and in such installations the velocity of the air stream may vary over wide limits. The air bypass valve II in the air conduit. tends to maintain a uniform flow of air through the combustion chamber. Ifthe air velocity increases, the bypass valve It opens, permitting a larger quantity of air to flow directly through the air conduit formed by the crosstubes II and ll of the T-flttings. Furthermore, the larger quantity of air thus bypassing the combustion chamber, tends to coolthe thermostat petals 24 and hold the volume of air passed through the combustion chamber between desirable limits even though the air velocity varies over .a wide range. Also it should be observed that the continuously expanded form of the combustion chamber oflsets, in part, the tendency of the velocity of gases to increase due to temperature rise permitting more efllcient heat exchange. The reduction in velocity of gases below the condition obtaining without continuous expansion of the walls of the combustion chamber results in a higher pressure at the discharge end of the combustion chamber. The by-pass valve it tends to maintain a low pressure region in the discharge end of the air conduit so that the gases are drawn from the exhaust tube of the combustion chamber at relatively high velocity. When the by-pass valve is closed, the pressure in the discharge end of the air conduit is reduced heat, the manual switch 02 is closed. The thermostat switch II is set at a lower temperature than thermostat switch 83; consequently, it opens first. This does not cut off the operation of the they reach the scoop so that they have insufficient mass to be effectively deflected by the scoop into contact with the igniter. Thus, during the ignition period the igniter is intimately in contact with the fuel, but after ignition is more or less trol valve 22. However, the thermostat petals 24 air heater, but reduces the quantity of fuel supplied. If conditions are such that this reduced quantity of fuel is sufficient to raise the temperature of the air heater above the setting of the high heat thermostat 83, this thermostat then operates as a safety means and cuts off} the motor as wellas the solenoid valve 36, shutting off the air heater entirely.

At a suitable low point in the combustion chamber, that is, in the side of the shell 2, or in the closed end of the combustion cone 6, may be located a drain tube (not shown) to drain oil' any excess liquid fuel should the air heater operate any appreciable time before ignition.

Many other embodiments of the invention may be resorted to without departing from the spirit of the invention. I

I claim: i

.1. An air heater comprising: a tubular outer shell open at its ends, a tubular inner shell closed at its ends: radiator elements between said shells; a combustion cone disposed within said inner shell and forming an expanding inner combustion passage, said cone defining with said directed into the smaller end of said combustion cone.

a, reverted combustion chamber having means forming an adiacently disposed air intake passage and gas exhaust tube; an air duct defined in part vsaid combustion chamber means and radiator elements extendingfrom said combustion chamber means into said air duct; a fuel nozzle directed into said combustion chamber; an air conduit traversing said intake-passage and exhaust tube, and a bypass valve in said air conduit between said intake and exhaust tubes: and yieldable means tending to close said bypass valve to divert air from said air conduit into said intake tube for return through said. exhaust tube.

3. An air heater comprising: means defining a reverted combustion chamber, means forming a lateral air intake passage at one end and means forming a lateral exhaust tubefor gases at its other end, the ends of said combustion chamber and said passages and tube being disposed in adjacent relation; an air duct defined in part by said combustion chamber means for the transfer of heat from saidcombustion chamben to air flowing in said air ductya fuel nozzle directed into said combustion chamber; and-a thermostat valve in said exhaust tube, said thermostat valve normally throttling flow from said combustion chamber and adapted to open upon heating of said combustion chamber to increase the flow therethrough.

4. An air heater comprising: means defining a reverted combustion chamber with its ends adjacent each other, an intake tube communicating with one end of said chamber and an adja- 2. An air heater comprising: means defining I 8 bustbrchamber to air flowing in said air duct: an air intake tube intersecting the intake end of said combustion chamber tangentially to cause helical flow of air through said chamber: an exhaust tube from the outlet end of said combustion chamber in proximity to said intake tube: a fuel nozzle directed axially into said combustion chamber from its smaller end through the region of air intake from said air intake tube; an air conduit traversing said intake passage and exhaust tube, and a bypass valve in said air conduit between said intake and exhaust tubes: and yieldable means tending to close said bypass valve to divert air from said air conduit into said intake tube for return through said exhaust tube.

7'. An air heater comprising: means defining a reverted continuously expanding combustion chamber having intake and outlet ends in proximity to each other: an air duct defined in part by said,means for the transfer of heat from said combustion chamber to air flowing in said air duct: an, air intake tube intersecting the intake and of said combustion chamber tangentially to cause helical flow of air through said chamber; an exhaust tube from the outlet end of'said combustion chamber in proximity to said intake tube;

cently disposed exhaust tube communicating with the other end of said chamber; an air duct defined in part by said means for the transfer of heat from said combustion chamber to air flowing in said air duct; a fuel nozzle directed into said combustion chamber, and an air conduit traversing said intake and exhaust tubes; a pressure responsive air bypass valve in said air conduit between said intake and exhaust tubes; yieldable means tending to close said bypass valve to divert air into said intake tube for subsequent return to said air conduit through said exhaust tube; and a thermostat valve in said exhaust tube including temperature sensitive means projecting into saidair conduit, said thermostat valve tending when cool to throttle flow through said combustion chamber and when heated to permit increased flow through said combustion chamber.

5. An air heater comprising: means defining a reverted continuously expanding combustion chamber;'an air duct'surrounding said means, radiating elements extending from said means into said air duct for the transfer of heat from said combustion chamber to air flowing in said air duct; an air intake tube intersecting the smaller end of said combustion chamber tangentially to cause helical flow of 'air through said chamber; an exhaust tube from the larger and of said combustion chamber; and a fuel nozzle directed axially into said combustion chamber from its smaller end through the region of air intake from said air intake tube.

'6. An air heater comprising: means defining a reverted continuously expanding combustion chamber having intake and outlet ends in proximity to each other; an air ductdeflnedin partbysaid means for the transfer of heat from said coma fuelnozzle directed axially into said combustion chamber from its smaller end through the regionof air intake from said air intake tube, and an air conduit traversing said intake and exhaust tubes; a pressure responsive air bypass valve in said air conduit between said intake and exhaust tubes; yieldable means tending to'close said bypass valve to divert air into said intake tube for subsequent return to said air conduit through said exhaust tube: and a thermostat valve in said exhaust tube including temperature sensitive means projecting" into said air conduit, said thermostat valve tending when cool to throttle flow through said combustion chamber and when heated to permit increased flow through said combustion chamber.

8.- A construction as set forth in claim 3, wherein said thermostat valve comprises a supporting memberand bimetallic petals converging therefrom, said petals adapted to curl away from each other on heating to open the passage through said exhaust tube.

9. A construction as set forth in claim 7, whereexhaust tube.

WALLACE HOL'BROOK.

REFERENCES CITED The following references are oi record in the file of this patent:

UNITED STATES PATENTS Number Name Date 738,619 7 Matthews Sept. 8, 1903 1,670,819 Morris et al May 22, 1928 1,711,365 Summers Apr. 30, 1929 1,755,727 Cramer Apr. 22, 1930 1,923,614 Clarkson Aug. 22, 1933 2,097,255 Saha Oct. 26, 1937 2,112,391 Anxionnaz Mar. 29, 1938 2,292,339 Mayo Aug. 4, 1942 2,332,094 McCiollum Oct. 19, 1943 2,362,571 McCollum i Nov. 14, 1944 2,366,416 McCoilum Jan. 2, 1945 2,393,187 Holthouse Jan. 15, 1948 

